Variable-Voltage Self-Synchronizing Rectifier Circuits, Methods, and Systems

ABSTRACT

The present application teaches, among other innovations, methods and circuits for operating a B-TRAN (double-base bidirectional bipolar junction transistor). A base drive circuit is described which provides high-impedance drive to the base contact region on whichever side of the device is operating as the collector (at a given moment). (The B-TRAN, unlike other bipolar junction transistors, is controlled by applied voltage rather than applied current.) The preferred implementation of the drive circuit is operated by control signals to provide diode-mode turn-on and pre-turnoff operation, as well as a hard ON state with a low voltage drop (the “transistor-ON” state). In some but not necessarily all preferred embodiments, an adjustable low voltage for the gate drive circuit is provided by a self-synchronizing rectifier circuit. Also, in some but not necessarily all preferred embodiments, the base drive voltage used to drive the c-base region (on the collector side) is varied while the base current at that terminal is monitored, so that no more base current than necessary is applied. This solves the difficult challenge of optimizing base drive in a B-TRAN.

CROSS-REFERENCE

Priority is claimed from U.S. Applications 62/076,320 (IPC-225.P),62/100,301 (IPC-234.P), 62/130,470 (IPC-242.P), 62/162,907 (IPC-248-P),62/182,878 (IPC-257-P), 62/194,167 (IPC-257-P.1), and 62/185,543(IPC-258-P), all of which are hereby incorporated by reference.

This application is being filed simultaneously with two other relatedapplications: ______ (“Variable-Voltage Self-Synchronizing RectifierCircuits, Methods, and Systems”, IPC-225:), ______ (“Circuits, Methods,and Systems with Optimized Operation of Double-Base Bipolar JunctionTransistors”, IPC-234:), and ______ (“Operating Point Optimization withDouble-Base-Contact Bidirectional Bipolar Junction Transistor Circuits,Methods, and Systems”, IPC-258:), all of which are hereby incorporatedby reference in their entirety.

BACKGROUND

The present application relates to power switching methods, andparticularly to circuits and methods for operation of bipolar powerswitching transistors which have two distinct and independent baseconnections.

Note that the points discussed below may reflect the hindsight gainedfrom the disclosed inventions, and are not necessarily admitted to beprior art.

Published U.S. application US 2014-0375287 (which is hereby incorporatedby reference) disclosed a fully bidirectional bipolar transistor withtwo base terminals. Such transistors are referred to as “B-TRANs.” Thetransistor preferably uses the bulk of a semiconductor die as a baseregion, and has two emitter/collector regions on opposite faces of thedie. Two distinct base contact regions are also provided—one on eachface of the die. Thus, for example, with a p-type semiconductor die,each face would include an n+ emitter/collector region and a p-type basecontact region. Isolation trenches and peripheral field-limiting ringsare preferably also included, but in essence this is a four-terminalthree-layer device.

An example of this published structure is generally illustrated in FIG.6. In this Figure, both faces of a semiconductor die 610 carryemitter/collector regions 622 which form a junction with the bulksubstrate 610. Base contact regions 632 are also present on both faces.This example shows an npn structure, so the emitter/collector regions622 are n-type, and the base contact regions 632 are p-type. A shallown+ contact doping 624 provides ohmic contact from separate terminals EC1and EC2 (on the two opposite faces of the semiconductor die, in thisexample) to regions 622, and a shallow p+ contact doping 634 providesohmic contact from separate terminals B1 and B2 (on the two oppositefaces of the die) to regions 632. In this example, dielectric-filledtrenches 640 provide lateral separation between base contact regions 632and emitter/collector regions 622. (Note that a p-type diffused regionmay be added to reduce the series resistance between the emitter-to-basejunction and the base contact.) B-TRANs can provide significantly betterefficiency than is conventionally available for existing static transferswitches; for example, a 1200V B-TRAN has an expected system efficiencyof 99.9%.

Application US 2014-0375287 also describes some surprising aspects ofoperation of this kind of device. Notably: 1) when the device is turnedon, it is preferably first operated merely as a diode, and base drive isthen applied to reduce the on-state voltage drop. 2) Base drive ispreferably applied to the base nearest whichever emitter/collectorregion will be acting as the collector (as determined by the externalvoltage seen at the device terminals). This is very different fromtypical bipolar transistor operation, where the base contact is(typically) closely connected to the emitter-base junction. 3) Atwo-stage turnoff sequence is preferably used. In the first stage ofturnoff, the transistor is brought out of full bipolar conduction, butstill is connected to operate as a diode; in the final state of turnoffdiode conduction is blocked too. 4) In the off state, base-emittervoltage (on each side) is limited by an external low-voltage diode whichparallels that base-emitter junction. This prevents either of thebase-emitter junctions from getting anywhere close to forward bias, andavoids the degradation of breakdown voltage which can occur otherwise.

Since the B-TRAN is a fully symmetric device, there is no differencebetween the two emitter/collector regions. However, in describing theoperation of the device, the externally applied voltage will determinewhich side is (instantaneously) acting as the emitter, and which isacting as the collector. The two base contact terminals are accordinglyreferred as the “e-base” and “c-base”, where the c-base terminal is onthe side of the device which happens to be the collector side at a givenmoment.

FIGS. 3A-3F (taken from published application 2014-0375287) show anexample of the operating sequence as disclosed in that application.

FIG. 3A shows a sample equivalent circuit for one exemplary NPN BTRAN.Body diodes 312A and 312B can correspond to e.g. the upper and lower P-Njunctions, respectively. In, for example, the sample embodiment of FIG.1A, these can correspond to the junctions between emitter/collectorregions 104A and base regions 102A. Switches 314A and 314B can shortrespective base terminals 108A and 108B to respective emitter/collectorterminals 106A and 106B.

In one sample embodiment, a BTRAN can have six phases of operation ineach direction, as follows.

1) Initially, as seen in FIG. 3B, voltage on emitter/collector terminalT1 is positive with respect to emitter/collector terminal T2. Switches314A and 316A are open, leaving base terminal B1 open. Switch 314B isclosed, shorting base terminal B2 to emitter/collector terminal T2.This, in turn, functionally bypasses body diode 312B. In this state, thedevice is turned off No current will flow in this state, due to thereverse-biased P-N junction (represented by body diode 312A) at theupper side of the device.

2) As seen in FIG. 3C, the voltage on emitter/collector terminal T1 isbrought negative with respect to emitter/collector terminal T2. P-Ndiode junction 312A is now forward biased, and now begins injectingelectrons into the drift region. Current flows as for a forward-biaseddiode.

After a short time, e.g. a few microseconds, the drift layer iswell-charged. The forward voltage drop is low, but greater in magnitudethan 0.7 V (a typical silicon diode voltage drop). In one sampleembodiment, a typical forward voltage drop (Vf) at a typical currentdensity of e.g. 200 A/cm² can have a magnitude of e.g. 1.0 V.

3) To further reduce forward voltage drop Vf, the conductivity of thedrift region is increased, as in e.g. FIG. 3D. To inject more chargecarriers (here, holes) into the drift region, thereby increasing itsconductivity and decreasing forward voltage drop Vf, base terminal B2 isdisconnected from terminal T2 by opening switch 314B. Base terminal B2is then connected to a source of positive charge by switch 316B. In onesample embodiment, the source of positive charge can be, e.g., acapacitor charged to +1.5 VDC. As a result, a surge current will flowinto the drift region, thus injecting holes. This will in turn causeupper P-N diode junction 312A to inject even more electrons into thedrift region. This significantly increases the conductivity of the driftregion and decreases forward voltage drop Vf to e.g. 0.1-0.2 V, placingthe device into saturation.

4) Continuing in the sample embodiment of FIG. 3D, current continuouslyflows into the drift region through base terminal B2 to maintain a lowforward voltage drop Vf. The necessary current magnitude is determinedby, e.g., the gain of equivalent NPN transistor 318. As the device isbeing driven in a high level injection regime, this gain is determinedby high level recombination factors such as e.g. surface recombinationvelocity, rather than by low-level-regime factors such as thickness of,and carrier lifetime within, the base/drift region.

5) To turn the device off, as in e.g. FIG. 3E, base terminal B2 isdisconnected from the positive power supply and connected instead toemitter terminal T2, opening switch 316B and closing switch 314B. Thiscauses a large current to flow out of the drift region, which in turnrapidly takes the device out of saturation. Closing switch 314A connectsbase terminal B1 to collector terminal T1, stopping electron injectionat upper P-N junction 312A. Both of these actions rapidly remove chargecarriers from the drift region while only slightly increasing forwardvoltage drop Vf. As both base terminals are shorted to the respectiveemitter/collector terminals by switches 314A and 314B, body diodes 312Aand 312B are both functionally bypassed.

6) Finally, at an optimum time (which can be e.g. nominally 2 μs for a1200 V device), full turn-off can occur, as seen in e.g. FIG. 3F. Fullturn-off can begin by opening switch 314B, disconnecting base terminalB2 from corresponding terminal T2. This causes a depletion region toform from lower P-N diode junction 312B as it goes into reverse bias.Any remaining charge carriers recombine, or are collected at the upperbase. The device stops conducting and blocks forward voltage.

The procedure of steps 1-6 can, when modified appropriately, used tooperate the device in the opposite direction. Steps 1-6 can also bemodified to operate a PNP BTRAN (e.g. by inverting all relevantpolarities).

SUMMARY

The present application teaches, among other innovations, methods andcircuits for operating a B-TRAN, and modules and systems incorporatingsome or all of these innovations.

The present inventor has discovered, surprisingly, that when a B-TRAN isbeing operated in full-ON transistor mode (i.e. with low voltage dropand high current flow) the collector-side base contact (i.e. the“c-base”) has a high impedance, up to the point where the current flowon the c-base starts to increase significantly. At that point thetransistor is already operating with a very low voltage drop, andincreased c-base current will degrade gain without much improvement involtage drop.

The preferred base drive circuit operates as a voltage-source drive tothe c-base (i.e. to the base contact on whichever side of the device isoperating as the collector at a given moment). The preferredimplementation of the drive circuit is operated by control signals toalso provide diode-mode turn-on and pre-turnoff operation.

In some but not necessarily all preferred embodiments, two separatesubcircuits are used, on each of the bases, for drive in differentmodes: one subcircuit provides an adjustable voltage for c-base drive infull-ON transistor mode, and the other subcircuit clamps one or bothbases to the corresponding emitter/collector regions in diode-on mode orin pre-turnoff mode.

In some but not necessarily all preferred embodiments, power for thebase drive circuit is provided by a self-synchronizing rectifiercircuit.

Also, in some but not necessarily all preferred embodiments, the basedrive voltage used to drive the c-base region (on the collector side) isvaried while the base current at that terminal is monitored, so that nomore base current than necessary is applied. This avoids reduced gain,and solves the difficult challenge of optimizing base drive in a B-TRAN.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosed inventions will be described with reference to theaccompanying drawings, which show important sample embodiments and whichare incorporated in the specification hereof by reference, wherein:

FIG. 1A shows one exemplary embodiment of a base drive circuit accordingto the present inventions.

FIG. 1B shows one sample embodiment of a base drive circuit according tothe present inventions.

FIG. 1C shows exemplary waveforms during operation of the embodiment ofFIG. 1A.

FIG. 2 shows one sample embodiment of a variable-voltageself-synchronous rectifier.

FIGS. 3A, 3B, 3C, 3D, 3E, and 3F show sample equivalent circuits for anexemplary B-TRAN in various stages of operation.

FIG. 4 shows a partial device model according to one sample embodimentof the present inventions.

FIG. 5 shows how the base current I_(CB) on the c-base varies withc-base bias V_(CB) under operating conditions.

FIG. 6 shows one sample embodiment of a B-TRAN.

DETAILED DESCRIPTION OF SAMPLE EMBODIMENTS

The numerous innovative teachings of the present application will bedescribed with particular reference to presently preferred embodiments(by way of example, and not of limitation). The present applicationdescribes several inventions, and none of the statements below should betaken as limiting the claims generally.

Published PCT application WO2014/210072 (which is hereby incorporated byreference) disclosed (inter alia) novel bidirectional bipolartransistors known as “B-TRANs.” As discussed above, the operating cycleof a B-TRAN includes, in succession, a “diode turn-on” (or “diode-ON”)state, a low-V_(ce) or “transistor-ON” state, a “pre-turnoff” state, andan “active OFF” state. Preferably the B-TRAN also has a “passive-OFF”state, which keeps its blocking voltage high when normal operation isnot happening.

The present application describes improvements in the operation of thesedevices. One area of improvement has been in the fully ON state (the“transistor-ON” state). An important advantage of the B-TRAN is its lowvoltage drop V_(CE) when fully on. However, it is desirable to maintaina high value for device gain. It is also desirable to keep the device'sswitching speed and reverse recovery fast. These improvements have beenachieved by a better understanding of the device's behavior in the fullyON state.

For simplicity, the following description will assume that an NPN B-TRANis being used. In this case the physical base is provided by the bulk ofthe p-type semiconductor die, and the base contact regions are p-type(with p+ contact doping). The two emitter/collector regions are n+, andwhichever emitter/collector region sees a more positive external voltagewill be the collector side. (The principles of operation are the samefor PNP B-TRAN devices, with opposite polarity; in such devices the sidewhich sees the more negative external voltage will be the collectorside.)

The base contact region on the collector side will be referred to as the“c-base,” and the other base contact region (on the emitter side) willbe referred to as the “e-base.” These base contact regions are notphysically different, but behave very differently when an externallyapplied voltage is present.

The fully ON state (transistor-on) is reached by applying elevated drivevoltage to the c-base. This provides a low on-state voltage drop withgood gain, without reducing the breakdown voltage. Device gain ismeasured as beta, i.e. the ratio of emitter current to base current, butthe behavior of the transistor under c-base drive is very different fromthat of other power bipolar junction transistors.

FIG. 4 shows a partial device model, with a table of values for c-basebias V_(CB) and corresponding voltage drop V_(CE) across the externalterminals. In this figure, the collector/emitter terminal at the top ofthe figure is assumed to be the collector (i.e. connected to the morepositive external voltage), so the base contact which is shown connectedto the variable voltage source is the c-base.

FIG. 5 shows how the base current I_(CB) on the c-base varies withc-base bias V_(CB) under operating conditions. It should be noted thatcurrent I_(CB) is nearly flat over a wide range of values for V_(CB).

The combination of FIGS. 4 and 5 shows important features of operation.The device's voltage drop V_(CE) will come down to its desired low valuewhen c-base bias V_(CB) gets up to its optimal operating point (definedas described below), but the current on the c-base stays nearly constantas c-base bias is increased to this point. To put this differently, thec-base terminal has a very high impedance until its bias is increased tothe point where the impedance drops. At this point, the device's seriesresistance is low, as desired.

In the transistor-on state, the e-base is essentially at a constantvoltage—it varies only about 0.1 V from a low drive to a high drivecondition. The c-base, in contrast, is a nearly constant current drive,even as the voltage is varied from 0 V above the collector to about 0.6Vabove the collector. Instead of the c-base current changing with c-basevoltage, V_(CE) changes. At a c-base bias of 0V (c-base shorted tocollector), there is a certain gain that depends on the emitter currentdensity, and Vce is nominally 0.9 V over a large range of currentdensity. Raising the c-base bias to 0.1 V above the collector does notchange the gain, but it lowers Vce by nominally 0.1 V. Raising c-basebias to 0.6V drops Vce to about 0.2 or 0.3 V. Thus, when driving thec-base, a voltage source is advantageously used, as in the sampleembodiment of FIG. 1A, not a current source.

This is a very significant difference from the way BJTs are normallydriven, which is from a current source into the base.

The differential impedance, in terms of di/dv, of the c-base itself ishigh. The c-base drive current changes very little with c-base tocollector voltage V_(CB) over a wide range of values, until V_(CB) getsclose to forward biasing the collector/base junction (over 0.6V at 25Cin silicon). That is why a voltage-source-type drive is needed. C-basecurrent I_(CB) changes with emitter current, increasing with increasedemitter current even when V_(CB) remains constant, but not much withchanging V_(CB) (up until a value of V_(CB) where I_(CB) begins toincrease undesirably).

The impedance of the e-base is very low, as it keeps a nearly constantvoltage while the c-base current is varied.

FIG. 1A shows a first example of a complete switch 100, including an NPNB-TRAN transistor 106 as well as diode-mode drive circuitry 110 andtransistor-mode drive circuitry 130. The half at the top of the pagewill be assumed to be the collector side, i.e. to be seeing the positiveside of the applied voltage.

FIG. 1C shows an example of waveforms during the operation of thecircuit of FIG. 1A. Initially, in the diode-on phase, the gate of NMOSS12 is low, and the gate of NMOS S13 is high. This enables thediode-turn-on mode described e.g. in published applicationUS2014-0375287. NMOS transistors S22 and S23 remain off. During thistime the current I_(T) across the emitter/collector terminals turns onquickly, and voltage V_(CE) across the emitter/collector terminals,which is assumed to have been ramping up under external drive, isbrought down to approximately a diode drop (plus some ohmic drop, for atotal of about 0.8V in silicon).

Next, in the transistor-on phase, S12 is turned on while S13 is turnedoff S12 is connected to a variable-voltage source 190, which is derivedfrom the collector terminal as described below. This voltage at thec-base drives the transistor into its low-voltage-drop state, where thevoltage drop V_(CE) is 0.3V or less. This phase continues for as long asdrive current is needed.

In the pre-off phase, switch S12 is turned off, and switches S13 and S23are both turned on. This immediately bumps the voltage drop up to adiode drop, but the device current I_(T) remains at a level determinedby emitter current density. If this current is not enough to clamp thevoltage of the external load, the applied voltage will increase asshown.

Finally, in the active-off phase, switch S13 is turned off, but switchS23 remains on. This cuts off device current I_(T), and the voltage onthe device goes up to whatever is dictated by the external connections.

Note that switch S23 was never turned on during this sequence. Thisswitch would be turned on to achieve the transistor-on mode when theexternal voltage has reversed (so that the emitter/collector terminalnode at the top of the page is then the emitter side rather than thecollector side).

FIG. 2 shows one sample embodiment of a variable-voltageself-synchronous rectifier, which can be advantageously used in thesample embodiment of FIG. 1A. A variable-voltage supply 210 (which inthe example shown is a simple buck converter) provides an adjustablesupply voltage to oscillator 220. Oscillator 220 drives a first winding232 of a transformer 230. A first secondary winding 234 providescomplementary outputs A and B, which are synchronous with thetransitions of oscillator 220, plus the phase shift due to couplingthrough the transformer 230. Another secondary winding 236 provides ahigher-current and lower-voltage waveform, corresponding to the outputof oscillator 220 (with voltage shifted). The output of the twosecondary windings is synchronous, so that the control signals A and Bcan be used to drive the synchronous inverter 240. The control signals Aand B are preferably scaled to provide appropriate gate voltages for thefour transistors of the synchronous inverter, e.g. 5V. Thus a 24V DCsupply has been efficiently translated into a very-low-voltage DC outputwhose voltage can be varied. By changing the set-point voltage of thebuck converter, the voltage applied to the c-base terminal can beadjusted.

Returning now to FIG. 5, the bias on the c-base terminal is optimized byadjusting it to the point where base current is no longer constant.

Unlike the e-base contact, the c-base contact is high impedance, meaningthat the current I_(CB) going into the c-base is nominally constant,when the device is on, until V_(CB) gets close to forward biasing thebase-collector junction. At that point, V_(CE) is well below a diodedrop (nominally 0.2V), and I_(CB) starts increasing rapidly with smalladditional increases in V_(CB), as shown below.

The present application teaches, among other concepts, that V_(CB) isdynamically varied, or “dithered”, to find the Optimal Operating Point.The Optimal Operating Point should fall where I_(CB) has increased somesmall but measurable amount above the flat portion of the I_(CB)/V_(CB)curve. This is done by finding a V_(CB) where the slope of the curve issome optimal value.

In one sample embodiment, the optimal value for the “transconductance”,or the optimal operating point, is when the base drive current is 20%over the base drive current for the c-base to collector shortedcondition V_(CB)=0 V. This point can be found, in practice, by anynumber of dithering sequences; in one example a baseline value forI_(CB) can be found in diode mode, and then a target value iscalculated, e.g. by increasing the baseline current value by 10% or 20%or 30%. Voltage V_(CB) is then increased in small steps, e.g. in 1%increments, until the measured collector current reaches the targetvalue. Optionally two limit values can be calculated, and the controlvoltage V_(CB) ramped back down when the upper limit value for I_(CB) isreached during operation. Optionally this dithering process can berepeated at short intervals when the transistor is in the ON state forlong periods of time.

FIG. 1B shows an example of a more complete base drive circuit. This isslightly different from the drive circuit of FIG. 1A in thatantiparallel diodes are connected with the body diodes in two of the MOStransistors in the diode-mode drive circuitry 110. Moreover, FIG. 1Balso shows the JFET plus Schottky branches which form the passive-offprotection circuitry 120.

A B-TRAN is in the “active off-state” when the e-base (base on emitterside) is shorted to the emitter, and the c-base (base on the collectorside) is open. In this state with the NPN B-TRAN, the collector is theanode (high voltage side), and the emitter is the cathode (low voltageside).

The B-TRAN is also off when both bases are open, but due to the highgain of the B-TRAN in this state, the breakdown voltage is low. Theseries combination of a normally-ON JFET and a Schottky diode attachedbetween each base on its respective emitter/collector, as previouslydisclosed, will significantly increase the blocking voltage in this“passive off-state”. The JFETs are turned off during normal operation.

One presently-preferred sample embodiment for B-TRAN turn-on is tosimultaneously, from the active off-state and blocking forward voltage,open the e-base to emitter short while shorting the c-base to thecollector. This immediately introduces charge carriers into the highestfield region of the depletion zone around the collector/base junction,so as to achieve very fast, forward biased turn-on for hard switching,very similar to IGBT turn-on.

Another advantageous turn-on method, from the active off-state, occurswhen the circuit containing the B-TRAN reverses the polarity of thevoltage applied to the B-TRAN, which produces the same base statedescribed in the hard turn-on method, but at near zero voltage. That is,the e-base which is shorted to the emitter becomes the c-base shorted tothe collector as the B-TRAN voltage reverses from the active off-statepolarity. Again, turn-on is fast.

In a third turn-on method from the active off-state, the e-base isdisconnected from the emitter, and connected to a current or voltagesource of sufficient voltage to inject charge carriers into the baseregion. This method is likely slower, since the charge carriers go intothe base just below the depletion zone. Also, it is known that carrierinjection into the e-base results in inferior gain relative to carrierinjection into the c-base.

After turn-on is achieved with either of the methods using the c-base,Vce is more than a diode drop. To drive V_(CE) below a diode drop,turn-on goes to the second stage of increased charge injection into thec-base via a voltage or current source. The amount of increased chargeinjection determines how much V_(CE) is reduced below a diode drop.Injection into the e-base will also reduce V_(CE), but the gain is muchlower than with c-base injection.

Turn-off can be achieved by any of several methods. The mostadvantageous method is a two-step process. In the first step, the c-baseis disconnected from the carrier injection power supply and shorted tothe collector, while the previously open e-base is shorted to theemitter. This results in a large current flow between each base and itsemitter/collector, which rapidly removes charge carriers from the driftregion. This in turn results in a rising Vce as the resistivity of thedrift region increases. At some optimum time after the bases areshorted, the connection between the c-base and the collector is opened,after which Vce increases rapidly as the depletion region forms aroundthe collector/base junction.

Alternately, turn-off can be achieved by simply opening the c-base andshorting the e-base to the emitter, but this will result in higherturn-off losses since the drift region (base) will have a high level ofcharge carriers at the start of depletion zone formation.

Or, turn-off can be achieved by simply opening the c-base and leavingthe e-base open, but this will result in the highest turn-off losses andalso a low breakdown voltage.

In one sample embodiment, the base drive uses only N-channel MOSFETs todrive the B-TRANs. This makes advantageous use of low MOSFET outputvoltage (less than 0.7V). The input is most preferably variable voltage,which, with current sensing, can be used to determine the optimum basedrive voltage.

Another sample embodiment can support higher voltages, but uses bothN-channel and P-channel MOSFETs.

Advantages

The disclosed innovations, in various embodiments, provide one or moreof at least the following advantages. However, not all of theseadvantages result from every one of the innovations disclosed, and thislist of advantages does not limit the various claimed inventions.

-   -   High gain;    -   Low ON-state voltage drop;    -   Avoidance of breakdown;    -   Inherent current limiting;    -   Simple circuit implementation;    -   Minimized power dissipation;    -   Adjustable supply voltage.

According to some but not necessarily all embodiments, there isprovided: The present application teaches, among other innovations,methods and circuits for operating a B-TRAN (double-base bidirectionalbipolar junction transistor). A base drive circuit is described whichprovides high-impedance drive to the base contact region on whicheverside of the device is operating as the collector (at a given moment).(The B-TRAN, unlike other bipolar junction transistors, is controlled byapplied voltage rather than applied current.) The preferredimplementation of the drive circuit is operated by control signals toprovide diode-mode turn-on and pre-turnoff operation, as well as a hardON state with a low voltage drop (the “transistor-ON” state). In somebut not necessarily all preferred embodiments, an adjustable low voltagefor the gate drive circuit is provided by a self-synchronizing rectifiercircuit. Also, in some but not necessarily all preferred embodiments,the base drive voltage used to drive the c-base region (on the collectorside) is varied while the base current at that terminal is monitored, sothat no more base current than necessary is applied. This solves thedifficult challenge of optimizing base drive in a B-TRAN.

According to some but not necessarily all embodiments, there isprovided: A system for power switching, comprising: a bidirectionalbipolar transistor which has two first-conductivity-typeemitter/collector regions separated by a bulk second-conductivity-typebase region, and two distinct second-conductivity-type base contactregions which connect to the bulk base region in mutually separatelocations; and first and second transistor-mode drive circuits,separately connected to the first and second base contact regionsrespectively; wherein each drive circuit is configured, as a voltagesource, to selectably apply an adjustable voltage between thecorresponding base contact region and the emitter/collector region whichis nearest to that base contact region; and first and second diode-modedrive circuits, separately connected to the first and second basecontact regions respectively; wherein each drive circuit is configuredto selectably connect the corresponding base contact region to theemitter/collector region which is nearest to that base contact region.

According to some but not necessarily all embodiments, there isprovided: A system for power switching, comprising: a bidirectionalbipolar transistor which has two first-conductivity-typeemitter/collector regions separated by a bulk second-conductivity-typebase region, and two distinct second-conductivity-type base contactregions which connect to the bulk base region in mutually separatelocations; and a pair of transistor-mode drive circuits, separatelyconnected to the first and second base contact regions respectively,wherein each transistor-mode drive circuit is a voltage-mode drivecircuit; and a pair of diode-mode drive circuits, separately connectedto the first and second base contact regions respectively; wherein eachdiode-mode drive circuit is configured to selectably connect thecorresponding base contact region to the emitter/collector region whichis nearest to that base contact region.

According to some but not necessarily all embodiments, there isprovided: A system for power switching, comprising: a bidirectionalbipolar transistor which has two first-conductivity-typeemitter/collector regions separated by a bulk second-conductivity-typebase region, and two distinct second-conductivity-type base contactregions which connect to the bulk base region in mutually separatelocations; and a pair of transistor-mode drive circuits, separatelyconnected to the first and second base contact regions respectively;wherein each drive circuit is configured, as a voltage source, toselectably apply an adjustable voltage at a selectable value between thecorresponding base contact region and the emitter/collector region whichis nearest to that base contact region.

According to some but not necessarily all embodiments, there isprovided: A method for power switching, comprising: driving abidirectional bipolar transistor which has two first-conductivity-typeemitter/collector regions in distinct locations separated by a bulksecond-conductivity-type base region, and two distinctsecond-conductivity-type base contact regions which connect to the bulkbase region in mutually separate locations, by in a transistor-ON mode,when minimal voltage drop is desired, using one of a pair of first drivecircuits to supply a selected adjustable voltage to the one of the basecontact regions which is closest to whichever of the emitter/collectorregions is positioned to act as the collector, as defined by externallyapplied voltage polarity; and in a diode-ON mode, when a diode dropacross the device is acceptable, using one of a pair of second drivecircuits to clamp one of the base contact regions to the respectivelynearest one of the emitter/collector regions; and in a preturnoff mode,using both of the pair of second drive circuits to clamp each of thebase contact regions to the respectively nearest one of theemitter/collector regions.

According to some but not necessarily all embodiments, there isprovided: A method for power switching, comprising: driving abidirectional bipolar transistor which has two first-conductivity-typeemitter/collector regions in distinct locations separated by a bulksecond-conductivity-type base region, and two distinctsecond-conductivity-type base contact regions which connect to the bulkbase region in mutually separate locations, by in a transistor-ON mode,when minimal voltage drop is desired, using one of a pair of first drivecircuits to supply a selected adjustable voltage to the one of the basecontact regions which is closest to whichever of the emitter/collectorregions is positioned to act as the collector, as defined by externallyapplied voltage polarity; and in a diode-ON mode, when a diode dropacross the device is acceptable, using one of a pair of second drivecircuits to clamp one of the base contact regions to the respectivelynearest one of the emitter/collector regions.

According to some but not necessarily all embodiments, there isprovided: A method for power switching, comprising: driving abidirectional bipolar transistor which has two first-conductivity-typeemitter/collector regions in distinct locations separated by a bulksecond-conductivity-type base region, and two distinctsecond-conductivity-type base contact regions which connect to the bulkbase region in mutually separate locations, by in a transistor-ON mode,when minimal voltage drop is desired, using one of a pair of first drivecircuits to supply a selected adjustable voltage to the one of the basecontact regions which is closest to whichever of the emitter/collectorregions is positioned to act as the collector, as defined by externallyapplied voltage polarity.

According to some but not necessarily all embodiments, there isprovided: A method of providing a variable-voltage low-voltage output,comprising the actions of: a) providing an adjustable voltage to supplyan oscillator; b) using the oscillator to apply an AC waveform to aprimary winding of a transformer; c) at one secondary winding of thetransformer, generating complementary control signals; and d) using thecomplementary control signals to operate a synchronous rectifier whichis connected to another secondary winding of the same transformer, tothereby provide a low-voltage output.

According to some but not necessarily all embodiments, there isprovided: A variable-voltage low-voltage power circuit, comprising: anadjustable voltage supply circuit, connected to provide an adjustablevoltage; an oscillator circuit, connected to receive the adjustablevoltage as a supply voltage, and connected to drive a primary winding ofa transformer with an AC waveform; a first secondary winding of thetransformer, connected to output complementary control signals; and asecond secondary winding of the transformer, having fewer turns than thefirst secondary winding; and a synchronous rectifier, including at leastfour transistors which are gated by the complementary control signalsand are connected in a bridge configuration, which is connected torectify the output of the secondary winding; wherein the output of thesecond secondary winding, after rectification by the synchronousrectifier, provides a substantially DC output which is smaller than adiode drop.

According to some but not necessarily all embodiments, there isprovided: A method of operating a bidirectional bipolar transistor whichhas first and second first-conductivity-type emitter/collector regionsin distinct locations separated by a bulk second-conductivity-type baseregion, and also has two distinct second-conductivity-type base contactregions which connect to the bulk base region in mutually separatelocations, in respective proximity to first and second emitter/collectorregions but not to each other, comprising the actions of: a) when lowon-state resistance is desired, applying a base drive voltage towhichever of the base contact regions is then on the collector side ofthe device; and b) varying the base drive voltage while monitoring basecurrent, to thereby find a target base drive voltage where base currentbegins to increase with base drive voltage; and operating the transistorat approximately the target base drive voltage.

According to some but not necessarily all embodiments, there isprovided: A system for power switching, comprising: a bidirectionalbipolar transistor which has two first-conductivity-typeemitter/collector regions separated by a bulk second-conductivity-typebase region, and two distinct second-conductivity-type base contactregions which connect to the bulk base region in mutually separatelocations; and a pair of transistor-mode drive circuits, separatelyconnected to the first and second base contact regions respectively;wherein, during the transistor-ON state where low voltage drop isdesired, one of the drive circuits, as determined by external voltagepolarity, is configured to apply an adjustable voltage to a selected oneof base contact regions, and dither the adjustable voltage, to therebyfind an operating point voltage where the current at the selected basecontact begins to increase with applied voltage, and then keep theadjustable voltage at approximately the operating point voltage.

Modifications and Variations

As will be recognized by those skilled in the art, the innovativeconcepts described in the present application can be modified and variedover a tremendous range of applications, and accordingly the scope ofpatented subject matter is not limited by any of the specific exemplaryteachings given. It is intended to embrace all such alternatives,modifications and variations that fall within the spirit and broad scopeof the appended claims.

For one example, the main embodiments described above use NPN B-TRANtransistors. However, the same principles apply to PNP B-TRANtransistors, with appropriate inversion of voltages.

For another example, the teachings here can be applied to B-TRAN devicesof various sizes, depending on what blocking voltage and currentcapacity are required.

For another example, a wide variety of other sensors and/or controlrelationships can be added onto the conceptual circuit relations shownin this application.

For another example, where a B-TRAN is used as part of a larger circuit(e.g. a PPSA converter), a single control module can optionally beconnected to apply the appropriate control signals to each of theB-TRANs' drive circuits.

For another example, because voltage-mode drive is used, a single B-TRANdrive circuit can optionally be used to drive multiple B-TRANs inparallel. This is not practical with other bipolar junction transistors.

None of the description in the present application should be read asimplying that any particular element, step, or function is an essentialelement which must be included in the claim scope: THE SCOPE OF PATENTEDSUBJECT MATTER IS DEFINED ONLY BY THE ALLOWED CLAIMS. Moreover, none ofthese claims are intended to invoke paragraph six of 35 USC section 112unless the exact words “means for” are followed by a participle.

The claims as filed are intended to be as comprehensive as possible, andNO subject matter is intentionally relinquished, dedicated, orabandoned.

What is claimed is:
 1. A method of providing a variable-voltagelow-voltage output, comprising the actions of: a) providing anadjustable voltage to supply an oscillator; b) using the oscillator toapply an AC waveform to a primary winding of a transformer; c) at onesecondary winding of the transformer, generating complementary controlsignals; and d) using the complementary control signals to operate asynchronous rectifier which is connected to another secondary winding ofthe same transformer, to thereby provide a low-voltage output.
 2. Themethod of claim 1, wherein the complementary control signals aregenerated by a tapped winding with a grounded center terminal.
 3. Avariable-voltage low-voltage power circuit, comprising: an adjustablevoltage supply circuit, connected to provide an adjustable voltage; anoscillator circuit, connected to receive the adjustable voltage as asupply voltage, and connected to drive a primary winding of atransformer with an AC waveform; a first secondary winding of thetransformer, connected to output complementary control signals; and asecond secondary winding of the transformer, having fewer turns than thefirst secondary winding; and a synchronous rectifier, including at leastfour transistors which are gated by the complementary control signalsand are connected in a bridge configuration, which is connected torectify the output of the secondary winding; wherein the output of thesecond secondary winding, after rectification by the synchronousrectifier, provides a substantially DC output which is smaller than adiode drop.